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A resonant Two Body System for a point absorbing Wave Energy Converter with direct-driven linear generator
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2011 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, no 12, 124904- p.Article in journal (Refereed) Published
Abstract [en]

Based on an earlier conceptual model of a two body system point absorbing wave energy converter tuned to resonance in Swedish west coast sea states, an extended coupled hydrodynamic, mechanic, and electromagnetic model has been developed. The hydrodynamic characteristics of the two body system are studied in the frequency and time domain, while its response to real Swedish west coast sea states are studied in the time domain, by using a wave energy converter model with two independently moving bodies connected to a direct driven linear generator with non-linear damping. The two body system wave energy converter gives nearly 80% power capture ratio in irregular waves. The resonant behaviour is shown to be sensitive to the shape of the spectrum, and the distance between the two bodies is shown to have a large effect on the power absorption.

Place, publisher, year, edition, pages
2011. Vol. 110, no 12, 124904- p.
Keyword [en]
direct energy conversion, linear machines, resonant power convertors, wave power generation
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-160032DOI: 10.1063/1.3664855ISI: 000298639800142OAI: oai:DiVA.org:uu-160032DiVA: diva2:447851
Available from: 2011-10-13 Created: 2011-10-13 Last updated: 2017-12-08
In thesis
1. Hydrodynamic Modelling for a Point Absorbing Wave Energy Converter
Open this publication in new window or tab >>Hydrodynamic Modelling for a Point Absorbing Wave Energy Converter
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Surface gravity waves in the world’s oceans contain a renewable source of free power on the order of terawatts that has to this date not been commercially utilized. The division of Electricity at Uppsala University is developing a technology to harvest this energy. The technology is a point absorber type wave energy converter based on a direct-driven linear generator placed on the sea bed connected via a line to a buoy on the surface.

The work in this thesis is focused mainly on the energy transport of ocean waves and on increasing the transfer of energy from the waves to the generator and load. Potential linear wave theory is used to describe the ocean waves and to derive the hydrodynamic forces that are exerted on the buoy. Expressions for the energy transport in polychromatic waves travelling over waters of finite depth are derived and extracted from measured time series of wave elevation collected at the Lysekil test site. The results are compared to existing solutions that uses the simpler deep water approximation. A Two-Body system wave energy converter model tuned to resonance in Swedish west coast sea states is developed based on the Lysekil project concept. The first indicative results are derived by using a linear resistive load. The concept is further extended by a coupled hydrodynamic and electromagnetic model with two more realistic non-linear load conditions.

Results show that the use of the deep water approximation gives a too low energy transport in the time averaged as well as in the total instantaneous energy transport. Around the resonance frequency, a Two-Body System gives a power capture ratio of up to 80 percent. For more energetic sea states the power capture ratio decreases rapidly, indicating a smoother power output. The currents in the generator when using the Two-Body system is shown to be more evenly distributed compared to the conventional system, indicating a better utilization of the electrical equipment. Although the resonant nature of the system makes it sensitive to the shape of the wave spectrum, results indicate a threefold increase in annual power production compared to the conventional system.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 91 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 878
Keyword
Ocean wave energy, Point absorber, Wave energy converter, Wave energy transport, Polychromatic wave, Linear generator, Resonance, Finite depth, Modelling
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Marine Engineering Oceanography, Hydrology, Water Resources
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-160319 (URN)978-91-554-8214-5 (ISBN)
Public defence
2011-12-09, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2011-11-17 Created: 2011-10-21 Last updated: 2011-11-23Bibliographically approved

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Engström, JensKurupath, VenugopalanIsberg, JanLeijon, Mats

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